Trials and Informing Regional Farmers about Organic Weed Control Methods

General Comments

With trials like these, often the question is: What treatment is the best or the winner? The answer to this is depending on farm needs; water conservation, good harvest, weed control, overall labor costs and/or to build soil fertility.

Clearly the treatment areas that used a crimped cover crop had much less weed pressure, 70%-80% less weeds. Typically the areas where the winter cover was crimped in place to form a mulch had some perennial hardy weeds that had overwintered and had to be hand-weeded out. This was one to four weeds per 3’ x 100’ test area.

Clearly the crimped cover crop areas used 28% less water to achieve the same soil moisture as the areas where the cover crop was turned under before planting. The water needs changed during the season from 40% less water for the crimped areas in the first of the season to 14% less water late in the season. It is assumed that plant shade of larger plants late in the season made this difference.

Clearly the crimped areas slowed the release of available N more evenly over the growing season, with the cover crop turned under areas peaked in available N one month after tillage and after planting.

Clearly the two treatments with off-farm organic mulch added performed the best in weed control and added the most fertility to the soil, but labor costs were the highest for or about equal with hand weeding. The mulch was obtained free from the power company, which would be hard to obtain free mulch for larger areas.

Harvest sizes seemed to be similar in all the areas, except for squash plant, and harvest size was 25% less on the crimped areas. Rhoads has noticed this in years past that summer squash seems typically be smaller in plant size and harvest in crimped areas. This is assumed to be about soil looseness for these relatively shallow rooted plants. More testing needs to be done with many different types of squash, melons, cucumbers, etc....

Tomato yield was 15% higher on the crimped areas, but a week later for the main harvest than the bare earth areas. More testing is needed.

Corn harvest was similar, with the bare earth treatment areas having stalks averaging 4” taller, but ear size the same in crimped and non crimped areas. (This is assumed to a faster growth rate early in the season and or the bare earth areas did receive a bit more sunlight.)

Chile plant harvest and plant size were similar on the crimped areas and bare areas, but the crimped treatment areas suffered about 10% transplant loss due to grasshoppers while the non crimped areas lost only about 4% of the plants. (The grasshoppers liked the crimped areas, even though the non-crimped areas were adjacent to the crimped ones. Whether this was due to habitat/cover for the grasshoppers or the crimped areas were their hatching ground is unknown. Other local farmers reported suffering similar grasshopper damage to chiles this year.)

General comments on each of the seven treatment areas

No winter cover crop and mechanical/hand weeding

One of the observations was that in winter and spring winds in NM, bare areas lose soil, especially lighter in weight organic matter. The areas with the winter cover crop would actually pick up or hold wind blown dust. The crimped areas continued this all season long, after strong winds dust was held in the cover and mulch of the crimped cover.

In terms of winter planting and care, obviously the test area with no cover crop was the easiest to care for, except for some of the top soil lost. There was about 5% more weeding in this area; I suspect due to the allopathic or weed seed suppressing nature of the rye winter cover crop used in the other areas. The entire test area of both cover crop and non cover crop had dried seed free chicken manure applied in August of the year before. The area with no cover crop had the same amount of available N early in the season. But available N at the end of the season was the least for this treatment area.

A winter cover crop turned under before planting and mechanical/hand weeding

This is still a very viable growing method for certain crops given that labor costs are low. This area required three passes of hand- or hoe-weeding, and then weeds were allowed to grow but not to come to seed. This treatment and the mulch treatment were the most labor intensive, being about the same. There was no measurable difference in water needs of the area that did and did not have a cover crop turned under. It would be thought that more organic material in the soil would retain more water, but it was not measurable.

A winter cover crop turned under and an off-farm mulch (powerline chipper mulch)

The winter cover crop was turned under and approximately 3-4” of powerline wood chips was applied. This area was one of the winners in least amount of water and best harvest size. In terms of labor, the labor to apply a mulch is about the same as doing three hand weedings, but the mulch builds soil and at the end of the year had more available N than any other treatment, except the similar mulch over the crimped cover in treatment 7. This treatment produced the best squash harvests: 33% more squash than other treatments.

A winter cover turned under with organic herbicides for weed control

The organic herbicides will not kill all NM weeds, especially sheep’s head. Otherwise, if used in the germination phase, they do an excellent job at 10% less expense than hand weeding. This treatment and treatment number 6 both required one pass through hand weeding.

A winter cover crop crimped into a mulch and no weeding

The three crimped areas, this treatment and number 6 and 7, performed very well in having 70% less weeds throughout the entire season, using 27% less water and having good harvest in all crops except squash which seems to not like the no-till method as much. This was the winner in terms of least amount of labor and least amount of farm expenses. The labor of crimping is similar to one pass through in hand weeding. In order to have no weeds produce seed, this area had one very quick weeding several weeks after crimping to deal with several perennial weeds, and one quick weeding near mid-season to eliminate the few weeds that did germinate through the crimped cover. Unfortunately this treatment area, along with 6 and 7, did not suppress sheep’s head entirely.

A winter cover crop crimped with organic herbicides as weed control

This treatment was the overall best performer, but it still did require some brief hand weeding. It scored among the best with less water needed, average harvest sizes except with summer squash, better yields with tomatoes like the crimped and mulched areas, and the least amount of weeding and farm labor, and one of the best in terms of available N throughout the growing season.

A winter cover crimped and a mulch used as weed control

This treatment needed no weeding except for several perennial weeds early in the season and the sheep’s head that eventually later in the season grew in the mulch. It is thought that applying a mulch on top of the mulch of the crimped cover is too cost prohibitive in terms of farm labor, but it does virtually eliminate weeding. This area needed the least amount of water and did build soil, having better texture in the soil, more organic matter in soil testing (30% higher organic matter than the average.) and the most available N at season end, similar to the other mulched area that had the cover crop turned under instead of crimped into a above ground mulch.

What was Measured

Water use

The three crimped areas and the mulched area (treatments 7,6,5,3)

Over the season used 27% less water that the areas that had no cover crop or the cover crop turned into the soil before planting.
However the water savings diminished over the season, due to plant size giving more shade and less drying effect. Below is the water savings listed by month of the crimped and mulched areas.

May season 40% less water
June   34% less
July    20%
August 14% less

Harvest Size

Harvest size of the areas was similar, except Summer Squash had 25-33% smaller plants and harvest amount in the areas that had the cover crop crimped into a mulch. And tomatoes in the crimped areas and the mulched area were 15% more pounds but 5-9 days later in the main harvest than the non crimped and non mulched areas. Corn stalk size was about 4” taller in the non crimped areas, but ear size was similar. Chiles, like the tomatoes, were several days later in the crimped areas, but similar harvest counts and fruit size in crimped and non crimped areas. The chiles in the crimped area had more transplants (5% more) killed by grasshoppers and were replaced. The sunflower seeds did not germinate and were not replaced, but similar growth habits and plant size were seen in both crimped and non crimped areas in a few seeds that did germinate.  

Weeding Labor

The areas that were crimped averaged 70% less weeds than the conventional tilling areas, except for the tilled then mulched area performed similar. This 70% less weeds is a testament to this technique that not only suppresses weeds, but also builds soil, needs less water and holds soil in place during wind. Essentially this made for one hand weeding needed at transplanting time to kill the few remaining perennials that over wintered and one more selective hand weeding to kill the few weeds that were going to seed before harvest. These were quick ‘spot’ weedings. See Table for data.

Total Labor Weeding and Installing Weed Control

Labor results attempted to measure total time put into the weed control. The crimped areas took about 40% of the time to weed while suppressing 70% of the weeding needed for the conventional treatment areas. The extra time was spend in soil preparation for the cover crop and crimping the cover by hand. These savings could be better with a tractor crimper attached to a planter for one pass planting or transplanting. The weed control capabilities of the crimped areas compared well with the mulched areas. The mulched area over the crimped cover did not perform any better than the non mulched crimped areas. Essentially the crimped cover makes a sufficient in-place mulch to more than offset the costs and provides excellent suppression of most weeds, particularly early in the season when farmer time is more limited and seedling or transplants need low weed pressures that would severely limit crop size. Later in the season plants grow and shade the soil giving less weeds a chance to germinate.

Soil Fertility

The entire area was fertilized with dried chicken manure in August the year prior when planting the cover crop. The Hairy Vetch did not germinate and grow as well as the Winter Rye, due to a watering issue. Only about 20% of the vetch survived and was thin under the rye that grew well. There was no noticeable nitrogen (N) fixing that occurred. Trials with growing Hairy Vetch done at the Alcade Research Station demonstrated that vetch needed to be planted in August in order to make sufficient vegetative growth and produce N. Rye however can be planted later in the early fall. Sometimes cropping cycles dictate when a field is empty for that year and can be planted to a cover crop for the next season.

With monthly soil testing, what appears to be occurring is the rye cover ties up the N in the soil, then releases some of it right after crimping, then slowly after being crimped over the entire season. The N in the crimped and mulched areas rose the second month after crimping and planting slightly, obviously due to deterioration of the cover and mulch, but also might be attributed to increase soil activity due to warmer nights in those months. See table in this report for N numbers in each plot over season.

In the non crimped areas N responded as anticipated, with N high early in the season that peaked one month after planting and a fall off over the entire growing season with no additional sources of N being manufactured through decomposition. The peak in N one month after planting was likely due to the incorporation of the cover crop into the soil.

The area that did not receive a cover crop was adjacent to the area that had been cover cropped then tilled and showed similar N through the season. But this area was slightly downhill from the other test areas. It is assumed that if the non cover crop area was more separate that there would be differences shown in less N available.

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• Table of Field Data Results
• Germination of Cover crop Fall 2011
• Oct 3, 2011 Cover Growing
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• 5- Feb 2012
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